The book Eat Right for Your Type by Peter J. D’Adamo proposes that there are four different ideal diets, one for each blood type: A, B, AB, and O. Follow the diet that is ‘right for your type’, he says, and you can lose weight, cure ear infections, fight off cancer, heal yourself from Chronic Fatigue Syndrome, and much, much more. By ‘eating right for your type,’ D’Adamo asserts, you will be eating like your prehistoric ancestors did.70

This may sound very appealing. In a time when we have strayed so far from a natural way of eating, a guide to eating like your prehistoric ancestors could be quite helpful. And, indeed, many have been drawn in by D’Adamo’s promises.

But according to the Tufts University Health and Nutrition Letter, D’Adamo has his blood typing all wrong. “It’s a fallacy even to speak of ‘original’ type Os or ‘original’ type As because blood types did not originate with humans,” explains Dr Stephan Bailey, a nutritional anthropologist at Tufts University. “They came on the biologic scene long before humans did. Furthermore, there is no anthropologic evidence whatsoever that all prehistoric people with a particular blood type ate the same diet.”71

D’Adamo has come up with 16 different food groups, further divided into ‘Highly beneficial,’ ‘Neutral,’ and ‘Avoid’ foods, depending entirely on what blood type you are. Type As, for example, are told they do well on vegetarian diets, but they should avoid cabbage, potatoes, eggplant, olives, peppers, and tomatoes, among many other foods. They are, however, advised to eat snails.72

Type Os, on the other hand, are told to base their diets heavily around red meat. They are told to avoid oranges, apples, wheat, peanut butter, avocados, cabbage, and potatoes, but encouraged to eat veal, ground beef, and beef heart.

Many people who have tried D’Adamo’s diet have lost weight. There is a reason, but it isn’t the one he gives. In actuality, the diets recommended for all four blood types are each extremely low in calories. Some day’s plans have only 1,000 calories, half the caloric needs of an adult woman.

Nevertheless, for D’Adamo, virtually everything in life comes down to whether you are an A, B, AB, or O blood type. According to him, “(ABO) blood type can determine so many things: how much and how often we should eat; what our optimal daily schedule should be; what our best sleep/rest patterns are; how stress affects us and how to combat it; how to maximize our health; how to overcome disease; how we deal with aging; and even our degree of emotional well-being.”73

D’Adamo believes that people who are type O and type B must eat meat daily to be healthy. When confronted with the fact that vegetarian diets have been consistently shown to produce lower rates of cancer, heart disease, hypertension, diabetes, gallstones, kidney disease, obesity, and colon disease, and to enable people to live longer and more healthfully, he explains that type As do well on vegetarian diets. It is, however, mathematically impossible that the health advantages for vegetarians could be accounted for only by type As benefiting from the absence of meat. According to the Red Cross blood bank, the population of the United States is approximately 39 percent type A, 46 percent type O, 11 percent type B, and 4 percent type AB.74 There is no possible way that the consistent superiority of vegetarian diets that has been demonstrated repeatedly by world medical research could be due to vegetarian diets having health advantages only for type As, who are, after all, a minority of the population.

Similarly, D’Adamo’s explanation for the success of Dr Dean Ornish’s program of reversing heart disease, which includes putting people on a near-vegan diet with no meat, is that it has only worked for type As. It does not, he says, help type Os, type Bs, or type ABs.75

I asked Lee Lipsenthal, MD, the vice president and medical director of Dr Dean Ornish’s Preventive Medicine Research Institute, whether this might be possible. He replied,“There is no evidence in the scientific literature associating blood typology with nutrient needs. Although heart disease almost invariably gets worse, even when patients follow the American Heart Association recommendations, most of our patients have shown actual reversal of their disease, and the vast majority have shown measurable improvement in many areas – improved physical function on exercise tests, improved blood flow to the heart muscle, improved mood and sense of vitality, improved cholesterol levels, improved blood pressure, improved sleep patterns, and improved social function. We’ve had many hundreds of patients show dramatic improvements, and all this has been measured by objective tests. I don’t see any possibility that people with blood types 0 and B (who together represent nearly 60 percent of the population of the U.S.) are not being helped by the Ornish program.”76

D’Adamo believes that the risk of heart disease for type Os is reduced by eating meat.77 There is, however, no evidence in the world medical literature for this belief. The blood-type diet’s explanation for why type Os presumably need meat is that type Os do “well on animal products and protein diets – foods that require more stomach acids for proper digestion.” In fact, D’Adamo says that “type Os can efficiently digest meats because they tend to have high stomach acid content.”78

It is well known, however, that not all men and women with type O blood produce more hydrochloric (stomach) acid; some secrete normal levels and some have less than normal. Further, it is pepsin, not hydrochloric (stomach) acid, that is responsible for meat protein digestion. In people who have large amounts of hydrochloric acid, the stomach environment becomes unusually acidic. An especially acidic stomach actually make pepsin less effective at digesting protein.79

D’Adamo’s beliefs regarding the diets of early humans, likewise, seem to have no basis in fact. He writes, ‘The appearance of our Cro-Magnon ancestors in around 40,000 BC propelled the human species to the top of the food chain, making them the most dangerous predators on earth… (with) little to fear from any of their animal rivals… (and no) natural predators other than themselves. Protein – meat – was their fuel… By 20,000 BC Cro-Magnons had... decimated the vast herds of large game.”80

The foundation of D’Adamo’s blood-type theory is his belief that Cro-Magnons, who lived 40,000-20,000 years ago, were all type Os and ate mainly meat. Types A, B, and AB came along later, he says, and only they are genetically equipped for a diet that includes grains. There is no evidence anywhere in the scientific literature, however, that suggests Cro-Magnons were mainly or all type Os. Instead, there is considerable evidence that all four blood types existed in the time of the Cro-Magnons.

Were Cro-Magnons the heavy meat eaters D’Adamo portrays? Not according to paleontologist Richard Leakey, who is widely acknowledged as one of the world’s foremost experts on the evolution of the human diet. Leakey points out, “You can’t tear flesh by hand, you can’t tear hide by hand. Our anterior teeth are not suited for tearing flesh or hide. We don’t (and Cro-Magnons didn’t) have large canine teeth, and we wouldn’t have been able to deal with food sources that required those large canines.”81

In fact, says Leakey, even if Cro-Magnons had large canine teeth, they still almost certainly would only rarely have eaten meat. Their diet would have been similar to that of the chimpanzee, our closest genetic relative.

Molecular biologists and geneticists, Leakey says, have compared proteins, DNA, and the whole spectrum of biological features and have established very convincingly that humans are closer to chimpanzees than horses are to donkeys. This is remarkable, because horses and donkeys can mate and reproduce, although their offspring, mules, are sterile. A significant difference between humans and chimpanzees, though, is that chimpanzees have large canine teeth that can tear apart their prey, and have more strength and speed than humans. Still, even with these traits, which would be advantages for a meat-eater, chimpanzees, like other primates, eat a mainly vegetarian diet. Dr Jane Goodall, whose work with chimpanzees represents the longest continuous field study of any living creature in science history, says chimpanzees often go months without eating any meat whatsoever. Indeed, she says, “The total amount of meat consumed by a chimpanzee during a given year will represent only a very small percentage of the overall diet.”82

D’Adamo’s entire theory is based on his assumptions about the blood types and diets of our prehistoric ancestors. Even though his assumptions are wholly mistaken, however, his diet has been embraced by many in the naturopathic community, and some schools of naturopathic medicine have even begun to include this theory in their curriculum. As a result, some naturopaths are now recommending that vegetarians and vegans who are blood type O or B eat meat daily

However, other naturopaths decisively disagree. The founder of naturopathy, Dr Benedict Lust, called for “the elimination of… habits such as… meat eating.” Similarly, Henry Lindlahr, MD, whose work has been widely read in naturopathic colleges, defined naturopathy as favoring a ‘strict vegetarian diet.’ After a detailed and thorough discussion of the blood-type diet’s underpinnings, contemporary naturopaths Dr Deirdre B Williams and Dr John J McMahon conclude, “The blood type theory of diet doesn’t have a leg to stand on.”83

Footnote annotations can be found in the book The Food Revolution, How Your Diet Can Help Save Your Life and Our World.